It would be good to have a corner plot with all the distances/ RoCs. Also perhaps a Jacobian like done in this breathtaking and seminal work.
As Rana suggested, we present the scattering plot of the AS path mode matching for various variables. The plot is for the AS path, Plan 2 (whose params we summarize at the end of this entry).
In the corner plot, we color-coded each realization according to the mode matching. We use (purple, olive, grey) for (MM>0.99, 0.98<MM<=0.99, MM<=0.98), respectively. From the plot, we can see that it is most sensitive to the RoC of AS1. The plot also shows that we can compensate for some of the MM errors if we adjust the distance between AS1-AS3 (note that AS2 is a flat mirror). The telescope is quite robust to other errors.
The compensation requirement is further shown in the second plot. To correct for the 1% RoC error of AS1, we typically need to adjust AS1-AS3 distance by ~ 1 cm (if we want to go back to MM=1; the window for >0.99 MM spans also about 1 cm). This should be doable because the nominal distance between AS1-AS3 is 115 cm.
The story for plan1 is similar and thus not shown here.
AS path plan2 nominal params:
label z (m) type parameters
----- ----- ---- ----------
SRMAR 0 flat mirror none:
AS1 0.7192 curved mirror ROC: 2.5000
AS2 1.2597 flat mirror none:
AS3 1.8658 curved mirror ROC: -0.5000
AS4 2.5822 curved mirror ROC: 0.6000
OMCBS1 3.3271 flat mirror none:
label z (m) type parameters
----- ----- ---- ----------
SRMAR 0 flat mirror none:
AS1 0.7192 curved mirror ROC: 2.5000
AS2 1.2597 flat mirror none:
AS3 1.8658 curved mirror ROC: -0.5000
AS4 2.5822 curved mirror ROC: 0.6000
OMCBS1 3.3271 flat mirror none:
I've started a spreadsheet for the BHD optics specifications and populated it with my best initial guesses. There are a few open questions we still need to resolve, mostly related to mode-matching:
The spreadsheet is editable by anyone. If you can contribute any information, please do!
I've generated specifications for the new BHD optics. This includes the suspended relay mirrors as well as the breadboard optics (but not the OMCs).
To design the mode-matching telescopes, I updated the BHD mode-matching scripts to reflect Koji's draft layout (Dec. 2019) and used A La Mode to optimize ROCs and positions. Of the relay optics, only a few have an AOI small enough for curvature (astigmatism) and most of those do not have much room to move. This reduced the optimization considerably.
These ROCs should be viewed as a first approximation. Many of the distances I had to eyeball from Koji's drawings. I also used the Gaussian PRC/SRC modes from the current IFO, even though the recycling cavities will both slightly change. I set up a running list of items like these that we still need to resolve in the BHD README.
At a glance, all the specifications can be seen in the optics summary spreadsheet.
The LO beam originates from the PR2 transmission (POP), near ITMX. It is relayed to the BHD beamsplitter (and mode-matched to the OMCs) via the following optical sequence:
The resulting beam profile is shown in Attachment 1.
The AS beam is relayed from the SRM to the BHD beamsplitter (and mode-matched to the OMCs) via the following sequence:
A lens is used because there is not enough room on the BHD breadboard for a pair of (low-AOI) telescope mirrors, like there is in the LO path. The resulting beam profile is shown in Attachment 2.
Hang and I have reanalyzed the BHD telescope designs, with the goal of identifying sufficiently non-degenerate locations for ASC actuation. Given the limited room to reposition optics and the requirement to remain insensitive to small positioning errors, we conclude it is not possible put sufficient Gouy phase separation between the AS1/AS2 and LO1/LO2 locations. However, we can make the current layout work if we instead actuate AS1/AS4 and LO1/LO4. This would require actuating one optic on the breadboard for each relay path. If possible, we believe this offers the simplest solution (i.e., least modification to the current layout).
Radius of curvatures:
I successfully steered out the two output beams from BHD BS to ITMY table today. This required significant changes on the table, but I was able to bring back the table to balance coarsely and then recover YARM flashing with fine tuning of ITMY.
There is still an open issue with the BI channels not read by EPICS. They can still be read by the Windows machine though.
I looked into the issue that Yehonathan reported with the BI channels. I found the problem was with the .cmd file which sets up the Modbus interfacing of the Acromags to EPICS (/cvs/cds/caltech/target/c1auxey1/ETMYaux.cmd).
The problem is that all the channels on the XT1111 unit are being configured in Modbus as output channels. While it is possible to break up the address space of a single unit, so that some subset of channels are configured as inputs and another as outputs, I think this is likely to lead to mass confusion if the setup ever has to be modified. A simpler solution (and the convention we adopted for previous systems) is just to use separate Acromag units for BI and BO signals.
Accordingly, I updated the wiring plan to include the following changes:
So, one more Acromag XT1111 needs to be added to the c1auxey chassis, with the wiring changes as noted above. I have already updated the .cmd and EPICS database files in /cvs/cds/caltech/target/c1auxey1 to reflect these changes.
I added a new XT1111 Acromag module to the c1auxey chassis. I sanitized and configured it according to the slow machines wiki instructions.
Since all the spare BIOs fit one DB37 connector I didn't add another feedthrough and combined them all on one and the same DB37 connector. This was possible because all the RTNs of the BIOs are tied to the chassis ground and therefore need only one connection. I changed the wiring spreadsheet accordingly.
I did a lot of rewirings and also cut short several long wires that were protruding from the chassis. I tested all the wires from the feedthroughs to the Acromag channels and fixed some wiring mistakes.
Tomorrow I will test the BIs using EPICs.
I tested the digital inputs the following way: I connected a DB9 breakout to DB9M-5 and DB9M-6 where digital inputs are hosted. I shorted the channel under test to GND to turn it on.
I observed the channels turn from Disabled to Enabled using caget when I shorted the channel to GND and from Enabled to Disabled when I disconnected them.
I did this for all the digital inputs and they all passed the test.
I am still waiting for the other isolator to wire the rest of the digital outputs.
Next, I believe we should take some noise spectra of the Y end before we do the installation.
There was some work done on the Acro crate this morning. Unclear if this is independent, but I found that the IMC servo board IN1 slider doesn't respond anymore, even though I had tested it and verified it to be working. Patient debugging showed that BIO1 (and only that acromag unit with the static IP 192.168.114.61) doesn't show up on the subnet in c1psl. Hopefully it's just a loose network cable, if not we will switch out the unit in the afternoon.
Jon is going to make a python script which iteratively pings all devices on the subnet and we will put this info on an MEDM screen to catch this kind of silent failure.
Created 5-band BLRMS for seismometer data (Gur1, Gur2 and STS1 each in x,y,z respectively) and accelerometer 1 through 6.
each with a fitting 4th order butterworth bandpass.
Data is recorded at 256Hz as e.g. C1:PEM-ACC1_RMS_RMS_0p3_1_OUT_DQ. For the 75 channels we have that corresponds to the data rate of just 1.2 16kHz channels.
c1pem execution time increased fom 6-7us to 15-16us out of 480us available.
I fixed up the seismic.stp file for the StripTool display:
The BLRMS are totally crazy today! I'm not sure what the story is, since it's been this way all day (so it's not an earthquake, because things eventually settle down after EQs). It doesn't seem like anything is up with the seismometer, since the regular raw seismic time series and spectrum don't look particularly different from normal. I'm not sure what's going on, but it's only in the mid-frequency BLRMS (30mHz to 1Hz).
Here are some 2 day plots:
Its an increase in the microseismic peak. Don't know what its due to though.
I got two seismometers and one microphone back from Tara.
They are now near the Gurlap under the MC.
I have finally plugged GUR1 back in....it is down at ETMY for now, since that's where the cable was. BLRMS are back up on the projector.
BLRMS filters have been set up for the coil outputs and shadow sensor signals. The signals are sent to the C1PEM model from C1MCS, where I use the library block mentioned in the previous elog to put the filters in place. Some preliminary observations:
Unrelated to this work: we cleaned up the correspondence between the accelerometer numbers and channels in the C1PEM model. Also, the 3 unused ADC blocks in C1PEM (ADC0, ADC1 and ADC2) are required and cannot be removed as the ADC blocks have to be numbered sequentially and the signals needed in C1PEM come from ADC3 (as we found out when we tried recompiling the model after deleting these blocks).
In order to be consistent with the naming conventions for the new BLRMS filters, I made a library block that takes all the input signals of interest (i.e. for a generic optic, the coil signals, the local damping shadow sensors, and the Oplev Pitch and Yaw signals - so a total of 12 signals, unused ones can be grounded). The block is called "sus_single_BLRMS". Inside the block, I've put in 12 BLRMS library blocks, with each input signal going to one of them. All the 7 outputs of the BLRMS block are terminated (I got a compiling error if I did not do this). The idea is to identify the optic using this block, e.g. MC2_BLRMS. The BLRMS filters inside are called UL_COIL, UR_COIL etc, so the BLRMS channels will end up being called C1:SUS-MC2_BLRMS_UL_COIL_0p01_0p03 and so on. I tried implementing this in C1PEM, but immediately after compiling and restarting the model, I noticed some strange behaviour in the seismic rainbow STS strip in the control room - this was right after the model was restarted, before I attempted to make any changes to the C1PEM.txt file and add filters. I then manually opened up the filter bank screens for the RMS_STS1Z bandpass and lowpass filters, and saw that the filter switches were OFF - I wonder if this has something to do with these settings not being updated in the SDF tables? So I manually turned them on and cleared the filter hitsory for all 7 low pass and band pass filter banks, but the traces on the seismic striptool did not return to their nominal levels. I manually checked the filter shapes with Foton and they seem alright. Anyways, for now, I've reverted to the C1PEM model before I made any changes, and the seismic strip looks to be back at its normal level - when I recompiled and restarted the model with the changes I made removed, the STS1Z BLRMS bandpass and lowpass filters were ON by default again! I'm not sure what I'm doing wrong here, I will investigate this further.
As discussed in a Wednesday meeting some time ago, we don't need to be writing channels from BLRMS filter modules to frames at 16k (we suspect this is leading to the frequent daqd crashes which were seen the last time we tried setting BLRMS up for all the suspensions). EricQ pointed out to me that there conveniently exists a library block that is much better suited to our purposes, called BLRMS_2k. I've replaced all the BLRMS library blocks in the sus_single_BLRMS library block that I made with there BLRMS_2k blocks. I need to check that the filters used by the BLRMS_2k block (which reside in /opt/rtcds/userapps/release/cds/common/src/BLRMSFILTER.c) are appropriate, after which we can give setting up BLRMS for all the suspensions a second try...
We should make screens like this for the LSC signals, errors, ALS, etc.
I copied Mirko's PEM BLRMS block, and made it a library part. I don't know where such things should live, so I just left it in isc/c1/models. Probably it should move to cds/common/models. To make the oaf compile, you have to put a link in /opt/rtcds/caltech/c1/core/branches/branch-2.1/src/epics/simLink , and point to wherever the model is living.
I then put BLRMSs on the control signals coming into the OAF, and after the Correction filter bank in the Adapt blocks, so we can check out what we're sending to the optics.
Today I worked with the BLRMS channels, re-triangulated the seismometers (the STS is now on the very end of the Y-arm, while the GUR2 is on the X-arm - this GUR2 cable will need to be either extended or replaced - Jenne and I will look at parts tomorrow), and added 0.01 - 0.03 Hz and 0.03 - 0.1 Hz RMS channels (However, the MEDM files for these are not yet complete - I will finish these tomorrow) in order to be able to better see earthquakes. I also did some things for the neural network project, including beginning Simulink tutorials so that I can run my code by applying a force on a damped harmonic oscillator + white noise until it stops.
I will explain the methodology behind the new RMS filters tomorrow morning, when the seismometers have settled down and I can make coherence plots.
I'll post a better E-log tomorrow when it's not 2 in the morning.
I laid down the floor a BNC cable from the Y End table to the BNC Chamber. The cable runs next to the east wall.
I'm leaving the cable because it can turn useful in the future.
I'm tying the end of the cable to a big threaded steel rod on the side of the BS chamber.
I've also labeled as TRY
[Yuta, Steve, Manasa]
There are cables piled up around the access connector area which have been victims of stampedes all the time. I have heard these cables were somehow Den's responsibility.
Now that he is not around here:
I found piled up bnc's open at one end and with no labels lying on the floor near the access connector and PSL area. Yuta, Steve and I tried to trace them and found them connected to data channels. We could not totally get rid of the pile even after almost an hour of struggle, but we tied them together and put them away on the other side of the arm where we rarely walk.
There are more piles around the access connector...we should have a next cleanup session and get rid of these orphaned cables or atleast move them to where they will not be walked on.
I've checked that the 2pin lemo connector that was run some time ago from the LSC rack to the MC board does indeed transmit signals. To try and evaluate its suitability I did the following:
No real difference was seen between the two cases. The signal peak was the same height, width. 60Hz and harmonics were of the same amplitude. Here are the spectra out to 200k, they are very similar.
Mode cleaner was locked during this whole thing. This may interfere with the measurement, but is similar to the use case for the AO path. If ground loop / spurious noise issues keep occurring, it will be worthwhile to examine the noise of the CM and MC servo paths, inputs and outputs more carefully.
This evening, Gautam helped me with setting up the apparatus for calibrating the GigE for BRDF measurements.
The SP table was chosen to set up the experiment and for this reason a few things including a laser and power meter (presumably set up by Steve) had to be moved around.
We initially started by setting up the Crysta laser with its power source (Crysta #2, 150-190 mW 1064 laser) on the SP table. The Ophir power meter was used to measure the laser power. We discovered that the laser was highly unstable as its output on the power meter fluctuated (kind of periodically) between 40 and 150 mW. The beam spot on the beam card also appeared to validate this change in intensity. So we decided to use another 1064 nm laser instead.
Gautam got the LightWave NPro laser from the PSL table and set it up on the SP table and with this laser the output as measured by the same power meter was quite stable.
We manually adjusted the power to around 150 mW. This was followed by setting up the half wave plate(HWP) with the polarizing beam splitter (PBS), which was very gently and precisely done by Gautam, while explaining how to handle the optics to me.
On first installing the PBS, we found that the beam was already quite strongly polarized as there seemed to be zero transmission but a strong reflection.
With the HWP in place, we get a control over the transmitted intensity. The reflected beam is directed to a beam dump.
I have taken down the GigE(+mount) at ETMX and wired a spare PoE injector.
We tried to interface with the camera wirelessly through the wireless network extenders but that seems to render an unstable connection to the GigE so while a single shot works okay, a continuous shot on the GigE didn’t succeed.
The GigE was connected to the Martian via Ethernet cable and images were observed using a continuous shot on the Pylon Viewer App on Paola.
We deliberated over the need of a beam expander, but it has been omitted presently. White printer paper is currently being used to model the Lambertian scatterer. So light scattered off the paper was observed at a distance of about 40 cm from the sample.
While proceeding with the calibrations further tonight, we realized a few challenges.
While the CCD is able to observe the beam spot perfectly well, measuring the actual power with the power meter seems to be tricky. As the scattered power is quite low, we can’t actually see any spot using a beam card and hence can’t really ensure if we are capturing the entire beam spot on the active region of the power meter (placed at a distance of ~40cm from the paper) or if we are losing out on some light, all the while ensuring that the power meter and the CCD are in the same plane.
We tried to think of some ways around that, the description of which will follow. Any ideas would be greatly appreciated.
Thanks a ton for all your patience and help Gautam! :)
More to follow..
Power meter only needed to measure power going into the paper not out. We use the BRDF of paper to estimate the power going out given the power going in.
From what I understood froom my reading, [Large-angle scattered light measurements for quantum-noise filter cavity design studies(Refer https://arxiv.org/abs/1204.2528)], we do the white paper test in order to calibrate for the radiometric response, i.e. the response of the CCD sensor to radiance.‘We convert the image counts measured by the CCD camera into a calibrated measure of scatter. To do this we measure the scattered light from a diffusing sample twice, once with the CCD camera and once with a calibrated power meter. We then compare their readings.’
But thinking about this further, if we assume that the BRDF remains unscaled and estimate the scattered power from the images, we get a calibration factor for the scattered power and the angle dependence of the scattered power!
With this idea in mind, we can now actually take images of the illuminated paper at different scattering angles, assume BRDF is the constant value of (1/pi per steradian),
then scattered power Ps= BRDF * Pi cosθ * Ω, where Pi is the incident power, Ω is the solid angle of the camera and θ is the scattering angle at which measurement is taken. This must also equal the sum of pixel counts divided by the exposure time multiplied by some calibration factor.
From these two equations we can obtain the calibration factor of the CCD. And for further BRDF measurements, scale the pixel count/ exposure by this calibration factor.
NOTE: The potentiometers on the bread board circuit box (the one I have been using with the signal generator, DC power, LED displays, and pulse switches) is BROKEN!
The potential across terminals 1 and 2 (also 2&3) fluctuates wildly and there dial does not affect the potential for the second potentiometer (the one with terminals 4, 5, and 6).
This has been confirmed by Koji and Jaimie. PS I didn't break it! >____<
NEVERTHELESS, using individual resistors and the 500 ohm trim resistor, I have managed to get the current versus forward voltage plot for the Hamamatsu L9337 Infared LED
I labeled all the newly installed flanges and connected the in-air cables (40m/16530) to appropriate ports. These cables are connected to the CDS system on 1Y1/1Y0 racks through the satellite amplifiers. So all new optics now can be damped as soon as they are placed. We need to make more DB9 plugs for setting "Acquire" mode on the HAM-A coil drivers since our Binary input system is not ready yet. Right now, we only have 2 such plugs which means only one optic and be damped at a time.
We manually realigned the BS and PRM optical levers on the optical table.
I have restored the damping of BS and PRM. Today is janitor day. He is shaking things around the lab.
BS & PRM oplev is restored. Note: the F -150 lens was removed right after the first turning mirror from the laser. This helped Rana to get small spot on the qpd.
It also means that the oplev paths are somewhat different now.
Using PRX, I remeasured the relative actuation strengths of the BS and PRM to see if the PRM correction coefficient we're using is good.
My result is that we should be using MICH -> -0.2655 x PRM + 0.5*BS.
This is very close to our current value of -0.2625 x PRM, so I don't think it will really change anything.
The reason that the BS needs to be compensated is that it really just changes the PRM->ITMX distance, lx, while leaving the PRM-ITMY distance, ly, alone. I confirmed this by locking PRY and seeing no effect on the error signal, no matter how hard I drove the BS.
I then locked PRX, and drove an 804Hz oscillation on the BS and PRM in turn, and averaged the resultant peak heights. I then tried to cancel the signal by sending the excitation with opposite signs to each mirror, according to their relative meaured strength.
In this way, I was able to get 23dB of cancellation by driving 1.0 x PRM - 0.9416 * BS.
Now, in the PRMI case, we don't want to fully decouple like this, because this kind of cancellation just leaves lx invarient, when really, we want MICH to move (lx-ly) and PRCL to move (lx+ly). So, we use half of the PRM cancellation to cancel half of the lx motion, and introduce that half motion to ly, making a good MICH signal. Thus, the right ratio is 0.5*(1.0/0.9416) = 0.531. Then, since we use BS x 0.5, we divide by two again to get 0.2655. Et voila.
I tried to reduce BS 3.3 Hz motion with local damping. 3.3 Hz probably comes from the stack, but I want to reduce this because PRMI beam spot is moving in this frequency.
I tried it by putting some resonant gains to oplev servo and OSEM damping servo, but failed.
What I learned:
1. BS OSEM input matrix diagonalization looks impressively good. Below is the spectra of oplev pitch/yaw and OSEM pos/pit/yaw/side comparing with and without damping (REF is without). You can see mechanical resonances are well separated. Also, damping servos don't look like they are adding noise at 3.3 Hz.
2. 3.3 Hz motion is not stationary. Amplitude is sometimes high, but sometimes low. Amplitude changes in few seconds. You can even see 3.3 Hz in the dataviewer, too.
3. I set new oplev gains. I lowered them so that UGFs will be ~ 2.5 Hz. I turned ELP35 on.
C1:SUS-BS_OLPIT_GAIN = 0.2 (was 0.6)
C1:SUS-BS_OLPIT_GAIN = -0.2 (was -0.6)
4. All OSEM sensors feel about the same amount of 3.3 Hz motion.
5. OLPIT and OLYAW reduces if you put 3.3 Hz resonant gain to oplev servo, but it is maybe not true since they are in-loop error signals. You can't see the difference from OSEM sensors. Below is oplev pitch/yaw and OSEM pos/pit/yaw/side comparing with and without 3.3 Hz resonant gain (REF is without).
It is not as dramatic as PRMI, but I could see BS 3.3 Hz motion at AS and REFL when MI is locked at dark fringe.
Below is uncalibrated spectra of REFLDC and ASDC when
Red: MI is locked at dark fringe
Blue: there's no light (PSL shutter closed)
We have to do something to get rid of this.
[Anchal, Paco, Yuta]
I calibrated the BS oplev PIT and YAW error signals as follows:
The numbers are:
BS Pitch 15 / 130 (old/new) urad/counts
BS Yaw 14 / 170 (old/new) urad/counts
I bet the calibration is out of date; probably we replaced the OL laser for the BS and didn't fix the cal numbers. You can use the fringe contrast of the simple Michelson to calibrate the OLs for the ITMs and BS.
The numbers I have from the fitting don't agree very well with the OSEM readouts. Attachment #1 shows the Oplev pitch and yaw channels, and also the OSEM ones, while I swept the ASC_PIT offset. The output matrix is the "naive" one of (+1,+1,-1,-1). SUSPIT_IN1 reports ~30urad of motion, while SUSYAW_IN1 reports ~10urad of motion.
From the fits, the BS calibration factors were ~x8 for pitch and x12 for yaw - so according to the Oplev channels, the applied sweep was ~80urad in pitch, and ~7urad in yaw.
Seems like either (i) neither the Oplev channels nor the OSEMs are well diagonalized and that their calibration is off by a factor of ~3 or (ii) there is some significant imbalance in the actuator gains of the BS coils...
Need to double check against OSEM readout during the sweep.
[Suresh / Kiwamu]
Adjustment of the OSEMs on BS has been done.
All the bad suspensions (#5176) has been adjusted. They are waiting for the matrix inversion test.
The AS spot on the camera was oscillating at ~3 Hz. Looking at the Oplevs, the culprit was the BS PIT DoF. Started about 12 hours ago, not sure what triggered it. I disabled Oplev damping, and waited for the angular motion to settle down a bit, and then re-enabled the servo - damps fine now...
As part of the hunt why the X arm IR transmission RIN is anomalously high, I noticed that the BS Oplev Servo periodically kicks the optic around - the summary pages are the best illustration of this happening. Looking back in time, these seem to have started ~Nov 23 2020. The HeNe power output has been degrading, see Attachment #1, but this is not yet at the point where the head usually needs replacing. The RIN spectrum doesn't look anomalous to me, see Attachment #2 (the whitening situation for the quadrants is different for the BS and the TMs, which explains the HF noise). I also measured the loop UGFs (using swept sine) - seems funky, I can't get the same coherence now (live traces) between 10-30 Hz that I could before (reference traces) with the same drive amplitude, and the TF that I do measure has a weird flattening out at higher frequencies that I can't explain, see Attachment #3.
The excess RIN is almost exactly in the band that we expect our Oplevs to stabilize the angular motion of the optics in, so maybe needs more investigation - I will upload the loop suppression of the error point later. So far, I don't see any clean evidence of the BS Oplev HeNe being the culprit, so I'm a bit hesitant to just swap out the head...
The BS SIDE damping gain seemed too low. The gain had been 5 while the rest of the suspensions had gains of 90-500.
I increased the gain and set it to be 80.
I did the "Q of 5" test by kicking the BS SIDE motion to find the right gain value.
However there was a big cross coupling, which was most likely a coupling from the SIDE actuator to the POS motion.
Due to the cross coupling, the Q of 5 test didn't really show a nice ring down time series. I just put a gain of 80 to let the Q value sort of 5.
I think we should diagonalize the out matrices for all the suspensions at some point.
I have been working on analyzing the seismic data obtained from the 3 seismometers present in the lab. I noticed while looking at the combined time series and the gain plots of the 3 seismometers that there is some error in the calibration of the BS seismometer. The EX and the EY seismometers seem to be well-calibrated as opposed to the BS seismometer.
The calibration factors have been determined to be :
The seismometers each have 3 channels i.e X, Y, and Z for measuring the displacements in all the 3 directions. The X channels of the three seismometers should more or less be coherent in the absence of any seismic excitation with the gain amongst all the similar channels being 1. So is the case with the Y and Z channels. After analyzing multiple datasets, it was observed that the values of all the three channels of the BS seismometer differed very significantly from their corresponding channels in the EX and the EY seismometers and they were not calibrated in the region that they were found to be coherent as well.
Note: All the frequency domain plots that have been calculated are for a sampling rate of 32 Hz. The plots were found to be extremely coherent in a certain frequency range i.e ~0.1 Hz to 2 Hz so this frequency range is used to understand the relative calibration errors. The spread around the function is because of the error caused by coherence values differing from unity and the averages performed for the Welch function. 9 averages have been performed for the following analysis keeping in mind the needed frequency resolution(~0.01Hz) and the accuracy of the power calculated at every frequency.
The gain in the given frequency range is ~3. The phase plotting also shows a 180-degree phase as opposed to 0 so a negative sign would also be required in the calibration factor. Thus the calibration factor for the Y channel of the BS seismometer should be around ~3.
The mean value of the gain in the given frequency range is the desired calibration factor and the error would be the mean of the error for the gain dataset chosen which is caused due to factors mentioned above.
Note: The standard error envelope plotted in the attached graphs is calculated as follows :
1. Divide the data into n segments according to the resolution wanted for the Welch averaging to be performed later.
2. Calculate PSD for every segment (no averaging).
3. Calculate the standard error for every value in the data segment by looking at distribution formed by the n number values we obtain by taking that respective value from every segment.
The BS seismometer is a different model than the EX and the EY seismometers which might be a major cause as to why we need special calibration for the BS seismometer while EX and EY are fine. The sign flip in the BS-Y seismometer may cause a lot of errors in future data acquisitions. The time series plots in Attachment #4 shows an evident DC offset present in the data. All of the information mentioned above indicates that there is some electrical or mechanical defect present in the seismometer and may require a reset. Kindly let me know if and when the seismometer is reset so that I can calibrate it again.
The response of the BS actuator in a low frequency regime has been measured.
+ With free swinging MICH, the sensor (AS55_Q) was calibrated into counts/m.
=> The peak-peak counts was about 110 counts. So the sensor response is about 6.5x108 counts/m
+ Locked Michelson with AS55_Q and the signal was fedback to BS.
+ Set the UGF high enough so that the open loop gain below 10 Hz is greater than 1.
+ With DDT's swept sine measurement, C1:LSC-MICH_EXC was excited with a big amplitude of 40 counts.
+ Took a transfer function from C1:LSC-MICH_OUT to C1:LSC-MICH_EXC.
+ Calibrated the transfer function into m/counts by dividing it with the sensor response.
This seems like an error prone method for DC responses due to the loop gain uncertainty. Better may be to use the fringe hopping method (c.f. Luca Matone) or the fringe counting method
An update on calibration of the BS actuator : A fitting has been done.
Q and I aligned the BS such that we were hitting the center of ETMX. The ETMX cage does not have OSEM setscrew holes on the front, so it is not possible to put the targets that Steve made on this optic. So, I put the freestanding ruler in front of the optic, with the edge of the ruler at the center (as viewed from above) of the optic. Then Eric steered the BS until we were hitting the 5.5" mark, and roughly half of the beam was obscured by the ruler.
We then aligned ITMX such that the prompt reflection was colinear with the incoming beam.
I checked the 2 spots through the BS, heading to the AS port. (2 spots since MICH hasn't been locked / finely aligned yet). They were being clipped on the 2nd output PZT. I adjusted the knobs of the first output PZT to center the spots on the 2nd PZT. Note that the output PZTs' power is still off, and has been off for some unknown length of time. I had found them off when prepping for the vent a week or two ago. So the current alignment depends on them staying off. We don't really need them on until we're ready to employ our OMC.
The beams now look nicely unclipped on the AS camera, and we're aligning MICH.